JPH07267687A - Method for coating optical fiber - Google Patents

Abstract

PURPOSE:To provide a method for coating an optical fiber, capable of preventing adhesion of a deposit to be a hindering cause of process.quality in a secondary coating device, smoothing a coating process in a spinning process and forming a high-quality optical fiber in a high-speed.continuous spinning process of optical fiber and to supply a device therefor. CONSTITUTION:In producing an optical fiber wire 11 by providing an uncoated wire 3 of optical fiber with a primary coating film 20 and curing to give a primary coated film 7, then providing the primary coated film with a secondary coating film 21 and curing, the curing of the primary coating film 20 is carried out so as to make gel fraction of the cured primary coating film <=50%. In curing the secondary coating film 21, the uncured part of the primary coating film 20 is cured together with the secondary coating film 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method of an optical fiber which is advantageously used in a high speed and long spinning process of an optical fiber, and particularly to a primary coating on a bare optical fiber during the spinning process. In the coating process of the optical fiber, which is applied and cured to form the primary coated optical fiber, and then the secondary coating is applied to the coated optical fiber, the volatile components that accompany the primary coated optical fiber can be obtained without requiring a special additional device or additional process. The present invention relates to a method for coating an optical fiber, which prevents a process and quality obstacle caused by adhering to a secondary coating device and enables a long and high-quality optical fiber to be manufactured at high speed.

[0002]

2. Description of the Related Art An optical fiber is usually a bare optical fiber,
First, it is first coated with a curable resin with a relatively low Young's modulus,
Then, it is secondarily coated with a curable resin having a relatively high Young's modulus to obtain an optical fiber strand. This coating process is performed as part of the optical fiber spinning process. An example of a conventional optical fiber spinning process is shown in FIG. In FIG. 2, the optical fiber preform 1 is melt-spun in a heating furnace 2 at about 2000 ° C., and the formed optical fiber bare wire 3 is introduced into a primary coating device 4 to be an ultraviolet curing type or a thermal curing type for primary coating. It is coated with a resin 5 such as a mold, and then is cured by a primary curing device 6 by irradiation with ultraviolet rays or heating to obtain a primary coated optical fiber 7. The primary coated optical fiber 7 is then introduced into a secondary coating device 8 and coated with a resin 9 for secondary coating, and then cured by a secondary curing device 10 to have an optical fiber having two layers of cured resin coating. It is the wire 11. This step is performed on a vertical line from the upper side to the lower side in order to avoid obstacles such as uneven thickness of the coating.

[0003]

Recently, as the production of optical fibers has become faster and longer, various problems have occurred in the above-mentioned coating process. As one of them, as shown in FIG. 3, when the primary coating optical fiber 7 is introduced into the secondary coating device 8, the nipple 12 of the secondary coating device 8 is introduced.
There is a problem that the deposit 14 adheres to the inner wall and the peripheral portion of the coating port 13 which is the introduction hole of the primary coated optical fiber 7 formed in the above. When the deposit 14 adheres to and accumulates on the inner wall of the coating port 13, the liquid coating resin 9 overflows from the coating port 13 or the coating die 1
Bubbles are mixed in the coating resin 9 extruded from the resin 5 to form voids in the secondary coating 16, which deteriorates the quality of the product and sometimes causes disconnection or the like, resulting in incapability.

In the primary coating step, the deposit 14 generates heat due to the heat of polymerization during the curing of the primary coating resin, and an unpolymerized component having a relatively low molecular weight is generated as a volatile component. It is considered that the particles reach the nipple 12 in a state of being accompanied by the surroundings, and are condensed on the inner wall of the coating port 13 and the periphery thereof. Even in the primary curing device, the volatile matter adheres to, for example, an ultraviolet lamp and causes an obstacle such as lowering its efficiency. Therefore, measures such as flowing a clean gas into the ultraviolet lamp irradiation chamber are provided. However, even when high-speed and long spinning is still performed, sufficient removal cannot be performed, and even the nipple 12 of the secondary coating device accompanies. Accumulation of the deposit 14 in the nipple 12 of the secondary coating device 8 has become a serious problem as the spinning speed and length are increased.

The present invention solves this problem,
The purpose is to prevent adhesion of deposits to the nipple of the secondary coating device, smooth the coating process, and add high-quality optical fiber, without adding any special device or process even during high-speed / long-spinning. An object of the present invention is to provide a method for coating an optical fiber to obtain a fiber strand.

[0006]

The above problems can be solved by curing the primary coating so that the gel fraction of the cured primary coating layer is 50% or less. It is particularly preferable that the gel fraction is in the range of 40% to 50%. In the above, when curing the secondary coating, it is preferable to cure the uncured portion of the primary coating together with the secondary coating. An ultraviolet curable resin is used for each of the primary coating and the secondary coating, and each curing is preferably performed by irradiation with ultraviolet rays. The curing of the primary coating at this time is preferably performed by adjusting the irradiation amount of ultraviolet rays so that the gel fraction of the primary coating after curing is 50% or less, preferably within the range of 40% to 50%. Further, the curing of the secondary coating at this time is preferably performed by adjusting the irradiation amount of ultraviolet rays so that the uncured portion of the primary coating is cured together with the secondary coating. Here, the gel fraction is the residual percentage of the resin component that is not extracted with methyl ethyl ketone.

[0007]

When the primary coating is cured so that the gel fraction of the primary coating is 50% or less, the volatile components accompanying the primary coated optical fiber are not substantially generated. Therefore, no deposits accumulate on the nipple of the secondary coating device.

The present invention will be described in detail below with reference to the drawings. In the following description, the same components as those of the conventional example described with reference to FIGS. 2 and 3 are designated by the same reference numerals, and the description thereof will be omitted or simplified. FIG. 1 shows a preferred embodiment of the optical fiber coating method of the present invention. First, in the primary coating device 4, the bare optical fiber 3 is coated with the ultraviolet curable resin 5, and then this primary coating 20 is cured in the primary curing device 6 by irradiation of ultraviolet rays to form the primary coated optical fiber 7. An ultraviolet curable resin 9 is coated in the secondary coating device 8, and the secondary coating 21 is cured in the secondary curing device 10 by irradiation of ultraviolet rays to manufacture the optical fiber element wire 11. At this time, the primary coating is cured by adjusting the irradiation amount of ultraviolet rays so that the gel fraction of the primary coating 20 after curing is 50% or less, preferably in the range of 40% to 50%. Further, when the secondary coating 21 is cured in the secondary curing device 10, the irradiation amount of ultraviolet rays is adjusted to cure the uncured portion of the primary coating 20 together with the secondary coating 21.

By this coating method of the optical fiber, the volatile matter accompanying the primary coating optical fiber 7 is not substantially generated, and therefore, even in the high speed / long drawing, the deposits are deposited on the nipple of the secondary coating device 8. Does not adhere. Moreover, the manufactured optical fiber element wire 11 has the primary coating 20 and the secondary coating 2
Since No. 1 is also sufficiently cured, there is no quality problem.

The reason why volatile matter is not substantially generated is that in the primary curing device 6, when the primary coating 20 is incompletely cured to such an extent that the gel fraction G thereof is 50% or less, heat generation due to polymerization heat is suppressed. As a result, it is considered that the volatile component derived from the low molecular weight monomer component is not generated around the primary coated optical fiber 7. However, when the gel fraction G is extremely low, the primary coating cannot be shaped. Therefore, it is preferably in the range of 25% to 50%, more preferably 40%.
Within 50%. Gel fraction G is 40% to 50%
Within the range, the shapeability of the primary coating is maintained even during high-speed spinning, and volatile matter is not generated.

Since the primary coating contains uncured portions, it is of course necessary to cure the uncured portions before obtaining the final optical fiber product. This curing can be performed by, for example, additionally irradiating ultraviolet rays after obtaining the optical fiber strands 11, but by adjusting the irradiation amount of ultraviolet rays in the secondary curing device 10, curing of the secondary coating can be performed. It is advantageous to do them simultaneously. The ultraviolet irradiation amount in each of the primary curing device 6 and the secondary curing device 10 can be adjusted by adjusting the output or the number of lamps of the respective ultraviolet lamps 22 or 23 installed therein. That is, the irradiation amount is adjusted to be smaller in the primary curing and larger in the secondary curing than the ultraviolet irradiation amount used in the conventional coating process.

The gel fraction G of the primary coating 20 can be measured as follows. A sample of the primary coated optical fiber 7 cured in the primary curing device 6 is sampled and its weight (W ₁ ) is measured. Next, this sample is put into a Soxhlet type extractor and extracted using methyl ethyl ketone as a solvent. After the extraction, the sample is vacuum dried and its weight (W
₂ ) Measure. Finally, the sample is heated in an electric furnace at 600 ° C. to decompose and remove the coating, and the weight (W ₃ ) of the sample which becomes a bare optical fiber is measured. At this time, gel fraction G%
Can be calculated according to the following equation.

[0013]

[Equation 1]

Although one embodiment of the present invention in which the ultraviolet curable resin is used as the coating material has been described above, basically the same can be done when a thermosetting resin is used as the coating material for the primary coating. However, the adjustment of the primary curing performed so that the gel fraction is 50% or less is performed not by the irradiation amount of ultraviolet rays but by the adjustment of the heat supply amount. If the coating material for the primary coating is a thermosetting resin, the coating material for the secondary coating is also preferably a thermosetting resin. This is because, in this case, the uncured portion of the primary coating can be cured together with the secondary coating when the secondary coating is cured by heating.

[0015]

【Example】

(Example) In the spinning process of the optical fiber shown in FIG.
The output of the ultraviolet lamp 22 in the primary curing device 6 shown in FIG. 1 is variously changed so that the gel fraction of the primary coating after curing is 50% or less, and in any case, the secondary curing device is changed. The output of the ultraviolet lamp 23 in 10 was adjusted to an amount sufficient to cure the uncured portion of the primary coating as well as the secondary coating, and drawing was performed.

(Comparative Example) As a comparative example, the same drawing as in the above-described example was carried out, but the output of the ultraviolet lamp 22 was adjusted so that the gel fraction of the primary coating after curing exceeded 50%.

(Drawing Operation) As the primary coating material, two kinds of ultraviolet curable resins A and B were used in both the examples and the comparative examples. Drawing speeds of 300, 500 and 8
It was changed in three steps of 00 m / m. The operation time (m) from the start of operation to the occurrence of a defect in the drawing operation was measured. Here, the defects in the drawing operation are as follows: (1) The secondary coating resin 9 overflows from the nipple 12 of the secondary coating device 8. (2) Voids are generated in the secondary coating 21 of the obtained optical fiber strand 11. (3) Broken wire. It is the case where any one or more of the above is recognized. Example 1
Table 1 shows the measurement results of Comparative Example 3 and Comparative Examples 1 to 3.

[0018]

[Table 1]

From the results of Table 1, the gel fraction of the primary coating was 5
In any of Examples 1 to 3 with 0% or less, at a high drawing speed of 500 m / m to 800 m / m, the operable time was 300 m to 188 m or more, while the gel fraction was 50. % In the case of Comparative Examples 1 to 3 exceeding 3%
At a drawing speed of 00 m / m to 500 m / m, the operable time was 180 m or less, and from this result, the method used in the example effectively removed volatile components, and the coating in the nipple of the secondary coating device was performed. It is clear that the kimono was prevented from adhering and high-speed, long-distance drawing operation was possible. Particularly in Examples 4 and 5, the gel fractions were 48% and 45, respectively.
%, When using either the ultraviolet curable resin A or B, long-time operation for 300 minutes or more was continued without trouble in high-speed drawing at 500 m / m.

[0020]

According to the optical fiber coating method of the present invention, the primary coating is cured so that the gel fraction of the primary coating after curing is 50% or less. Volatile components do not accompany the primary coated optical fiber, and therefore deposits do not adhere to the nipple of the secondary coating device.
High speed and long wire drawing is possible without adding special equipment. When the secondary coating is cured, if the uncured portion of the primary coating is cured together with the secondary coating, a fully cured coating is formed without adding a special step.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention.

FIG. 2 is a process chart showing an example of an optical fiber spinning process.

FIG. 3 is a cross-sectional view showing one aspect of a conventional optical fiber spinning process.

[Explanation of symbols]

3 ... Bare optical fiber, 4 ... Primary coating device, 5 ... Primary coating resin, 6 ... Primary curing device, 7 ... Primary coating optical fiber,
8 ... Secondary coating device, 9 ... Secondary coating resin, 10 ... Secondary curing device, 11 ... Optical fiber element wire, 20 ... Primary coating, 21
… Secondary coating.

Claims (3)

[Claims] 1. A primary coating is applied to a bare optical fiber to cure it to form a primary coated optical fiber, and then a secondary coating is applied to the bare optical fiber to produce an optical fiber element wire. The gel fraction of the primary coating after curing is 5
A method for coating an optical fiber, which is performed so as to be 0% or less. 2. The method for coating an optical fiber according to claim 1, wherein when the secondary coating is cured, the uncured portion of the primary coating is cured together with the secondary coating. 3. An ultraviolet curable resin is used as each of the primary coating and the secondary coating, and each of them is cured by irradiation with ultraviolet rays.
The method for coating an optical fiber according to.